When using devices with space-constrained touch-sensitive screens, users must often comprehend the content of large documents when only a small part of the document can be seen at one time. When correlated information is distributed either horizontally or vertically in such a document, as in a spreadsheet or a table, a user must scroll from left to right or from top to bottom, while viewing only parts of a row or a column at a time. Without any form of guidance or reference points, it is difficult for a user to comprehend relationships within information that is spatially separated in the document.
FIG. 1 illustrates a large document 101 with a table 100, where correlated information is shown on each line. The table is viewed using a viewport that is large enough to view only a portion of the table 100 at a time. To use the table, a user must know the relationship of data at either end of the lines. For example, to find out the total price 125 of a single pole switch 120, a user must scroll all the way from a start position viewport 105 including the item description column to an end position viewport 110 including the total price column. The inaccuracy of the scrolling operation from left to right causes the viewport 110 to follow a circuitous route 131 across the table 100. Scrolling is adversely affected by error introduced by using fingers on a touch screen, by accidental vertical scrolling movements of the visible area (the “viewport” 105, 110) and by a lack of reference points in certain areas of the document, such as area 127. The result is that it is not clear to the user which one of the displayed prices correlates to the single pole switch. This decreases usability, requires more time to comprehend information and increases the chance of error.
One approach used in solving this problem is to restrict the scrolling direction to either horizontal or vertical movement. Such an approach is implemented, for example, on Apple's iPhone. When the user begins a scrolling operation by tapping the touch screen and moving it, the system determines the main direction of scrolling. Once the main direction of scrolling is determined, the device will limit movement of the viewport to that direction and prevent accidental movement perpendicular to the main scrolling direction.
There is presently a need to overcome the above-described limitations of existing scrolling techniques for viewing large documents on space-constrained touch-sensitive screens.